| 摘要 |
<p>PROBLEM TO BE SOLVED: To locally increase the material ductility of a valve bridge so as to improve a thermal fatigue life by adding melted pure aluminum to the thermal stress concentration part of the valve bridge section of a cylinder head made of an aluminum alloy and setting the alloy element content and the impurity element content of this section to be lower than those of a cylinder head base metal. SOLUTION: A recessed part is formed by machining after casting in a valve bridge section (place between an intake hole 3 and an exhaust hole 5) as the thermal stress concentration part of a cylinder head 2 made of an aluminum alloy, melted pure aluminum having a purity of 99.9% or higher is added to this recessed part by laser thickening so as to form an added welded part 7a and then heat treatment is given to the cylinder head 2. Then, by cutting off the bulged part of the added welded part 7a, a high ductile layer 7 is formed in the valve bridge section. Thus, the ductility of the valve bridge section of the cylinder head 2 is increased more than that of the base metal, a thermal fatigue strength is increased and durability against peeling or the like of the added welded layer and a base station part is improved.</p> |
